Clarify previous parameter expression

[HansOlsson]

Closes #3074 Note: This is a pure clarification - it is not intended to change anything.

[HansOlsson]

Apart from the minor suggestions given, I wonder if this doesn't call for a more highlighted definition of clocked state variable:

Likely - but it seems a more complete rewrite is needed. Obviously the section called 'Clocked state variable' should clearly define it, but it should non-normatively also explain why.

The introduction hint that we don't need start-values for all clocked variables, but only for the clocked state variables; and in that sense they represent the state of the system. But it is a bit more complicated as we also have hold(x).

\begin{definition}[Clocked state variable]\label{def:clocked-state-variable}\index[clocked!state variable]\index{state variable!clocked}
A component expression which is not a parameter, and to which \lstinline!previous! has been applied.
\end{definition}

However, with such clear a definition just above the definition of previous, do we really need to repeat the definition under previous?

Likely not.

[HansOlsson]

Reformulated more as I noted that stating that the argument must be on the same clock, and that the start-value is returned before the first clock tick doesn't really make sense for a parameter-argument.

[henrikt-ma]

The current formulation looks good to me, but it would be good to also get an approving review from somebody more versed than I in the synchronous terminology.

[HansOlsson]

The current formulation looks good to me, but it would be good to also get an approving review from somebody more versed than I in the synchronous terminology.

True, but since we haven't gotten them by now - I assume there are no complaints.